Polyimide obtained by reacting tetracarboxylic acid dianhydride with diamine is hereafter to be widely used in areas where high-temperature stability is required, by virtue of its various excellent properties and good thermal stability. In addition to the excellent high-temperature stability, polyimide also has good mechanical strength, dimensional stability, flame lame retardance and electrical insulation and is broadly applied in the materials of electric and electronic appliances, aeronautics and space instruments and transport machinery. It is also used as the high-temperature adhesive of various high performance materials in these fields.
Conventional polyimide, however, normally has an excellent thermal stability with a poor melt-feasibility due to its high softening point. On the other hand, the resin developed for improving the melt-feasibility is inferior in high-temperature stability. Thus the performance of polyimide has both merits and drawbacks.
Generally in the use of conventional polyimide, for example, in film manufacture, wire coating, cover sheet or adhesive, the linear chain structure causes high-packing density between chains and limits the chain mobility even in high temperatures. Therefore, conventional polyimide has an excellent thermal stability like a thermoset, but has a poor melt-feasibility and poor adhesive properties. On the other hand, the melt-feasible polyimide, especially in adhesive use, has a lower glass transition temperature and softening point than conventional polyimide. So, melt-feasible polyimide has as a poor thermal stability and a high C.T.E. (Coefficient of Thermal Expansion).
In the polyimide adhesive or adhesive tape in IC package tapes, a good melt-feasibility and a good spreadability onto a substrate like an IC chip, a protective layer on an IC chip or a leadframe are necessary in the bonding process. After bonding, the excellent adhesive property and thermal stability of the adhesive even in subsequent high-temperature processes, such as wire bonding and epoxy molding, are very important to guarantee the semiconductor package reliability.